The energy consumed by the burgeoning computing infrastructure worldwide has recently drawn significant attention. While the focus of energy management has been on the data-center setting, attention has also been directed recently to the significant amounts of energy consumed by desktop computers in homes and enterprises. It is estimated that personal computers (PCs) and their monitors consume about 100 terawatt-hours (TWh) per year, which makes up about 3% of the annual electricity consumed in the U.S. Of this, 65 TWh/year is consumed by PCs in enterprises, which makes up about 5% of the commercial building electricity consumption. More particularly, a typical desktop PC consumes about 80-110 W when active and 60-80 watts (W) when idle, excluding the monitor, which adds another 35-80 W.
A common approach to reducing PC energy costs is to put a computer to sleep when it is idle. In view of this, multiple S (“sleep”) states have been defined as part of the Advanced Configuration and Power Interface (ACPI) standard. In particular, the S3 state (“standby”) suspends the machine's state to RAM, thereby cutting energy consumption to 2-3 W. The S3 state has the advantage of being much quicker to transition in and out of than S4 (“hibernate”), which involves suspending the machine's state to disk.